As transistor design is improved and evolved, the number of different types of transistors continues to increase. Multi-gate non-planar metal oxide semiconductor field effect transistors (MOSFETs), including double-gate non-planar MOSFETs (e.g., finMOSFETs) and tri-gate non-planar MOSFETs, are developed to provide scaled devices with faster drive currents and reduced short channel effects over planar MOSFETs.
Double-gate non-planar MOSFETs are FETs in which a channel region is formed in a thin semiconductor fin. The source and drain regions are funned in the opposing ends of the fin on either side of the channel region. Gates are formed on each side of the thin semiconductor fin, and in some cases, on the top or bottom of the fin as well, in an area corresponding to the channel region. FinMOSFETs are a type of double-gate non-planar FETs in which the fin is so thin as to be fully depleted.
Tri-gate non-planar MOSFETs have a similar structure to that of double-gate non-planar MOSFETs; however, the fin width and height are approximately the same so that gates can be formed on three sides of the channel, including the top surface and the opposing sidewalls. The height to width ratio is generally in the range of 3:2 to 2:3 so that the channel will remain fully depleted and the three-dimensional field effects of a tri-gate MOSFET will give greater drive current and improved short-channel characteristics over a planar transistor.
Static random access memory (SRAM) cells can employ such multi-gate non-planar MOSFETs. For example, 6T-SRAM cells have two multi-gate non-planar pass-gate transistors, two multi-gate non-planar pull-up transistors, and two multi-gate non-planar pull-down transistors.